Journal of SMT Article

Pb-free Alloy Silver Content and Thermal Fatigue Reliability of a Large Plastic Ball Grid Array (PBGA) Package

Authors: Richard Coyle, Heather McCormick, John Osenbach, P
Company: Alcatel-Lucent, Celestica, Inc., LSI Corp., and GE
Date Published: 1/30/2011   Volume: 24-1

Abstract: This paper presents the latest results from an on-going investigation of Pb-free solder joint microstructure and attachment reliability of a 680 I/O plastic ball grid array (PBGA). Previously published work compared the temperature cycling performance of Sn4.0Ag0.5Cu (SAC405) and SnPb solder assemblies as a function of dwell time using an IPC-9701 accelerated temperature cycling test (ATC). In the current study, the accelerated temperature cycling matrix is expanded to include two additional Pb- free alloys, SAC305 (3% Ag) and SAC105 (1% Ag). The SAC305 and SAC105 BGA components were assembled and tested using either a dissimilar SAC405 paste or a matching solder paste such as SAC305 ball with SAC305 paste. As in the previously published studies, the 0°C to 100°C accelerated temperature cycling (ATC) tests were conducted using 10, 30, and 60 minute dwell times.

The test results show that the thermal fatigue performance improved substantially with a higher Ag content BGA alloy. Surprisingly, assembly with the higher Ag solder paste resulted in a measureable though small increase in thermal fatigue performance of both the SAC305 ands SAC105. The characteristic fatigue lifetime was inversely proportional to the test dwell time, which is consistent with previously published findings on this BGA package as well as SAC solders in general.


Pb-free solder, Ag content, thermal fatigue, accelerated temperature cycling, dwell time.

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